In general, an injection molding machine is provided with a three-plate type injection apparatus which comprises front and rear plates and a pusher plate disposed between these two plates for reciprocation. The injection apparatus of this type needs a long distance between the front and rear plates, and includes an injection motor and a transmission mechanism operatively connecting the motor and the pusher plate, both the motor and the mechanism being located behind the rear plate. Accordingly, the three plate type injection apparatus requires a wide installation space, thus constituting a hindrance to the reduction in size of the injection molding machine.